Automated classification based on photo-realistic image/model mappings

ABSTRACT

Techniques are provided for increasing the accuracy of automated classifications produced by a machine learning engine. Specifically, the classification produced by a machine learning engine for one photo-realistic image is adjusted based on the classifications produced by the machine learning engine for other photo-realistic images that correspond to the same portion of a 3D model that has been generated based on the photo-realistic images. Techniques are also provided for using the classifications of the photo-realistic images that were used to create a 3D model to automatically classify portions of the 3D model. The classifications assigned to the various portions of the 3D model in this manner may also be used as a factor for automatically segmenting the 3D model.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/742,845, filed on Jan. 14, 2020 and entitled “AUTOMATEDCLASSIFICATION BASED ON PHOTO-REALISTIC IMAGE/MODEL MAPPINGS,” which isa continuation of U.S. patent application Ser. No. 15/626,104, filed onJun. 17, 2017 and entitled “AUTOMATED CLASSIFICATION BASED ONPHOTO-REALISTIC IMAGE/MODEL MAPPINGS,” now issued as U.S. Pat. No.10,534,962, both of which are incorporated herein by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates to automated classification and, morespecifically, to automated classification based on mappings betweenphoto-realistic images and 3D models constructed based on thephoto-realistic images.

BACKGROUND

To classify a digital photo-realistic image, a human can view thephoto-realistic image and then manually tag the photo-realistic imagewith descriptive metadata. The types of information provided in suchtags is virtually limitless. Common tags may indicate the names ofpeople in the photo-realistic image, the objects in the photo-realisticimage, and the location and/or event at which the photo-realistic imagewas captured. Manual tagging produces highly accurate tags, becausehuman brains are highly skilled at interpreting the content ofphoto-realistic images. However, manually tagging photo-realistic imagescan consume an inordinate amount of time, particularly when thecollection of photo-realistic images to be tagged is large.

To avoid the human effort required by manual tagging, techniques havebeen developed to automatically tag photo-realistic images with certaintypes of information. For example, digital cameras can automaticallystore some types of information with each photo-realistic image, such astime, date and GPS coordinates at the time at which the photo-realisticimage is captured. However, automatically tagging photo-realistic imageswith some types of information is not so straightforward.

Various techniques have been developed to automatically identify complexfeatures, such as human faces and objects, within photo-realisticimages. Such techniques include, for example, using photo-realisticimages that depict a particular type of object to train a machinelearning engine to recognize that type object in other photo-realisticimages. Once trained, the machine learning engine may predict thelikelihood that any given photo-realistic image contains the type ofobject in question. Once analyzed, those photo-realistic images that arepredicted to contain a type of object may be tagged with metadata thatindicates the object they depict. For example, a machine learning enginemay predict that the photo-realistic image of the front of a housedepicts a door, and that photo-realistic image (or a set of pixelswithin the photo-realistic image) may be tagged with the metadataindicating that a door is depicted in the photo-realistic image.

Unfortunately, classifications made by machine learning engines can beindefinite and imprecise. To reflect the indefinite nature of suchclassifications, the classification automatically assigned to an objectin an image may be a list of labels with corresponding “confidencescores”. For example, a trained machine learning engine may classify aparticular object in a particular image as: 45% bottle, 25% vase, 25%wine glass, 5% test tube. Thus, there is a need to improve the accuracyof automated classifications of photo-realistic images.

The approaches described in this section are approaches that could bepursued, but not necessarily approaches that have been previouslyconceived or pursued. Therefore, unless otherwise indicated, it shouldnot be assumed that any of the approaches described in this sectionqualify as prior art merely by virtue of their inclusion in thissection.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee.

In the drawings:

FIG. 1 is a flowchart illustrating steps for adjusting theclassification of a target region of a photo-realistic image, accordingto an embodiment;

FIG. 2 illustrates a panoramic photo-realistic image that may be used,in combination with associated depth/distance metadata, to create a 3Dmodel of a real-world space;

FIG. 3 illustrates six views, each of which contain an overlappingregion of a 3D model;

FIG. 4 illustrates a 3D model onto which view-classifications have beenprojected, according to an embodiment, where different classificationsare represented by different colors;

FIG. 5 illustrates a view (target region) whose classifications havebeen adjusted/improved using the technique illustrated in FIG. 1 ;

FIG. 6 is a block diagram of a computer system programmed to perform theclassification adjustment techniques described herein; and

FIG. 7 is an example of a photo that has undergone per instance,per-pixel segmentation.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however,that the present invention may be practiced without these specificdetails. In other instances, well-known structures and devices are shownin block diagram form in order to avoid unnecessarily obscuring thepresent invention.

GENERAL OVERVIEW

Techniques are described herein for increasing the accuracy of automatedclassifications produced by a machine learning engine. Specifically, theclassification produced by a machine learning engine for onephoto-realistic image is adjusted based on the classifications producedby the machine learning engine for other photo-realistic images thatcorrespond to the same portion of a 3D model that has been generatedbased on the photo-realistic images. For example, a 3D model of a housemay be created based on photo-realistic images taken at variouslocations within the house, in conjunction with associateddepth/distance metadata. The 3D model of the house may include multiplerooms. For a given room in the model, the photo-realistic images thatcorrespond to the room may have been assigned inconsistentclassifications. For example, assume that a room of the modelcorresponds to five photo-realistic images, where one of thephoto-realistic images was automatically classified as “dining room”,one of the photo-realistic images was automatically classified as“bedroom”, and three of the photo-realistic images were classified as“kitchen”. In this example, based on the fact that all fivephoto-realistic images map to the same room in the model, theclassification of the two photo-realistic images that were notclassified as “kitchen” may be changed to “kitchen”.

Further, the classifications of the photo-realistic images used tocreate a 3D model may be used to automatically classify portions of the3D model. For example, if the majority of the photo-realistic imagesthat correspond to a particular room in the model have beenautomatically classified as “kitchen”, then the room itself, within the3D model, may be tagged with the classification of “kitchen”. Thisimage-to-model projection of classifications can be done at any level ofgranularity. For example, rather than classify an entire room of amodel, the technique may be used to classify a mesh surface in the room(e.g. a face in the mesh of the 3D model) or an object in the room. As amore specific example, all photo-realistic images that map to aparticular object in the 3D model may have been classified as having a“vase” in the portion of the photo-realistic images that maps onto thatparticular object. Consequently, within the 3D model, that object may beautomatically classified as a vase.

Automated Classification of Photo-Realistic Images

As mentioned above, various techniques have been developed forautomatically classifying photo-realistic images One such techniqueinvolves the use of Artificial Neural Networks. One implementation ofthis technique, which assigns classifications to entire images, isdescribed atwww.nvidia.cn/content/tesla/pdf/machine-learning/imagenet-classification-with-deep-convolutional-nn.pdf.Another implementation of an Artificial Neural Network, referred to asMask R-CNN, detects objects in an image while simultaneously generatinga high-quality per-instance per-pixel segmentation. FIG. 7 is an exampleof a photo that has undergone per instance, per-pixel segmentation. MaskR-CNN is described, for example, in the document located atarxiv.org/pdf/1703.06870.pdf, the contents of which are incorporatedherein by reference. The specific technique used to make the initialclassifications may vary from implementation to implementation, and thetechniques described herein are not limited to any particular machinelearning engine.

The granularity at which the classifications are made by machinelearning engines may vary based on the nature of the classification. Forexample, an entire photo-realistic image may be tagged with “bedroom”,while specific regions within the photo-realistic image are tagged withmore specific labels, such as “bed”, “chair” and “vase”. The techniquesdescribed herein for improving the accuracy of such classifications maybe used at any level of granularity. Thus, for the purpose ofexplanation, the techniques shall be described with respect to adjustingthe classification of a “target region” of a “target photo-realisticimage”. However, that “target region” may be as large as the entirephoto-realistic image, or as small as individual pixels or sub-pixels ofthe target photo-realistic image.

Generating 3D Models from Photo-Realistic Images

Before the classification of a photo-realistic image can be improvedbased on the mapping between the photo-realistic image and a 3D model, a3D model must first be constructed based on the photo-realistic imagesand, optionally, associated depth/distance metadata. 3D modelsconstructed in this manner may take a variety of forms, including butnot limited to point clouds, meshes and voxels. Further, the 3D modelscan contain color data such as texture maps, point colors, voxel colorsetc. The classification enhancement techniques described herein are notlimited to any particular type of 3D model. Various techniques may beused to generate a 3D model based on a collection of photo-realisticimages. Such techniques are described, for example, in:

-   -   U.S. patent application Ser. No. 11/939,663 entitled “System and        method for 3d model generation”    -   U.S. patent application Ser. No. 13/776,688 entitled “Capturing        and aligning three-dimensional scenes”    -   U.S. patent application Ser. No. 13/148,173 entitled “Generating        three-dimensional models from images”        Each of these documents is incorporated herein, in its entirety,        by this reference.

Frequently, the photo-realistic images used to construct 3D models ofreal-world environments are panoramic and include various types ofmetadata used in the construction of the 3D models. The metadata used inthe construction of the 3D models may be available at the time thephoto-realistic images are captured. Alternatively, some or all of themetadata may be derived after capture using an alignment algorithm. Asan example of the metadata that may accompany photo-realistic images,each photo-realistic image may have associated spatial information thatindicates exactly where the photo-realistic image was captured, thefocal direction for the photo-realistic image (or for each portion ofthe photo-realistic image when the photo-realistic image is panoramic),etc. In addition, the metadata may include distance information, forexample indicating the distance of various pixels in the image from thespatial point from which the photo-realistic image was captured. Morespecifically, the depth information may include per-pixel depthinformation for some pixels of an image, and/or depth values at specificpoints relative to the image.

The techniques described herein for improving the classification ofimages and/or portions of 3D models are not limited to any particulartechnique for constructing those 3D models, as long as image-to-modelmappings can be determined.

Segmenting 3D Models

After a 3D model has been generated based on a collection of capturedphoto-realistic images, it is often useful to segment the model andassign labels to the segments. For example, assume that a 3D model of ahouse is constructed from photo-realistic images captured within andaround the house. Once created, it may be useful to segment the modelinto distinct rooms, specific surfaces (eg floors), and/or specificobjects (eg tables). Techniques are described hereafter for improvingthe accuracy of automatic segmentation of a 3D model and the automaticlabelling of segments of a 3D model by projecting the classifications ofphoto-realistic images used to construct the 3D model onto thecorresponding portions of the 3D model.

Existing techniques for segmenting 3D models that have been constructedbased on photo-realistic images of real-world environments aredescribed, for example, in:

-   -   U.S. patent application Ser. No. 11/265,772 entitled “Method of        database-guided segmentation of anatomical structures having        complex appearances”    -   U.S. patent application Ser. No. 13/776,688 entitled “Capturing        and aligning three-dimensional scenes”    -   U.S. patent application Ser. No. 14/743,748 entitled “Building a        three-dimensional composite scene”

Each of these documents is incorporated herein, in its entirety, by thisreference.

Source-Sets and Source Regions

Frequently, the collection of photo-realistic images used to construct a3D model includes panoramic photo-realistic images taken from a varietyof locations. For example, to create a 3D model of a house, panoramicphoto-realistic images may be captured at many different capture pointswithin each room of the house. Consequently, any given portion of themodel (e.g. wall, door, or table) may correspond to a real-world featurethat is depicted in multiple photo-realistic images within thecollection.

The set of photo-realistic images that depict the real-world featurethat corresponds to a given portion of a 3D model is referred to hereinas the “source-set” for that given portion of the 3D model. For example,assume that a 3D model of a house:

-   -   was constructed from 100 photo-realistic images    -   has a five doors    -   has a five rooms

Assume that one of the five doors is depicted (from differentviewpoints) in 3 of the 100 photo-realistic images. Those 3photo-realistic images qualify as the source-set for the portion of themodel that represents that door. Similarly, if 20 of thosephoto-realistic images depict different views of a particular room, thenthose 20 photo-realistic images are the source-set for the portion ofthe 3D model that represents that particular room.

The term “source-region” refers to the region, within each image in thesource-set, that corresponds to a particular portion of the 3D model.For example, a portion of a 3D model of a house may represent a room X.For photo-realistic images that depict only room X, the source-region isthe entire photo-realistic image. On the other hand, for photo-realisticimages that depict part of room X and part of other rooms, only theregion that depicts room X qualifies as the source-region for room X.

Aggregating Source-Region Classifications to Improve Classification of aTarget Region

Referring to FIG. 1 , it is a flowchart that illustrates how theclassification of a target region of a photo-realistic image may beimproved based on the source set of the portion of a 3D model thatcorresponds to the photo-realistic image. Referring to FIG. 1 , at step100 a 3D model is constructed based on a collection of photo-realisticimages. As explained above, any number of techniques may be used togenerate the 3D model, and the techniques described herein are notlimited to any particular model construction technique.

At step 102, each photo-realistic image in the collection ofphoto-realistic images used to construct the 3D model is automaticallyclassified using a trained machine learning engine. For the purpose ofillustration, it shall be assumed that the photo-realistic images are ofa real-world house, the 3D model is a model of the real-world house, andthe photo-realistic images are automatically classified to indicate (a)objects within the house (e.g. door, windows, furniture) and (b) theroom-type of the room depicted in the image. With respect to room-typeclassification, the room-type classification may take the form ofconfidence scores assigned to each room-type. For example, a particularphoto-realistic image A may be classified as having 60% probability ofbeing a kitchen, 30% probability of being a bedroom, 5% probability ofbeing a bathroom, 5% probability of being a dining room.

As mentioned above, the accuracy of such automated classifications isoften less than would be achieved by manual classification. Steps 104 to112 may be performed for one or more target regions of one or more ofthe photo-realistic images in the collection to improve the accuracy ofclassifications of those target regions. For the purpose of explanation,steps 104 to 112 describe classification adjustment where one targetregion of a photo is adjusted at a time. However, to improve efficiency,embodiments may adjust many images in a batch. When performed in abatch, the amalgamation of the individual image classifications may beused to determine the classification of a particular portion of the 3Dmodel. Then, those classifications are back-projected to the individualimages.

When classification adjustment is performed on a per-target-regionbasis, at step 104, a target region of a target photo-realistic image isselected for classification adjustment. For the purpose of illustration,it shall be assumed that the target region selected in step 104 is theentirety of a photo-realistic image A, and that the classification to beadjusted is the room-type classification (which is initially 60%kitchen, 30% bedroom, 5% bathroom, 5% dining room).

At step 106, the portion of the 3D model that maps to the target regionis determined. The portion of the 3D model to which the target regionmaps is referred to herein as the “target portion” of the 3D model. Theportion of the 3D model to which a given target region maps may bedetermined based on spatial location and orientation informationassociated with the target region, and spatial location and orientationinformation associated with the 3D model.

The granularity of the target portion of the model is dictated, in part,by the nature of the classification that is being adjusted. In thepresent example, since the classification at issue is a room-typeclassification, the target portion of the 3D model may be the room,within the model, to which the target photo-realistic image maps. Thus,in this example, the target portion of the model encompasses more thanmerely what is shown in the target region. Alternatively, for aroom-type classification, classifications may be separately assigned toeach mesh face in the room (e.g. each mesh face of the portion of the 3Dmodel that represents the room), rather than to the entire room. Whenroom-type classifications are made at the per-face level of granularity,the target portion of the model may be a single face, or each facedepicted in the target photo-realistic image may be separately processedas the “target portion”.

At step 108, the “source-set” for the target portion of the 3D model isdetermined. The source-set for the target portion of the 3D model is theset of photo-realistic images that depict the real-world content that isrepresented by the target portion of the 3D model. In the presentexample, the target portion of the 3D model is the room, within the 3Dmodel, that represents the room depicted in photo-realistic image A.That room shall be referred to herein as “room X”.

For the purpose of explanation, it shall be assumed that the source-setof room X includes photo-realistic images A to H. Once the source-set ofthe target portion of the model has been determined at step 108, thesource-regions within those source-set images are determined. Asmentioned above, the source-regions of a source-set image may includethe entire image, or a subset thereof. For the purpose of explanation,it shall be assumed that everything shown in images A to H correspond toroom X. Both the source-set and the source-regions are determined basedon a comparison of the spatial metadata (e.g. capture location,orientation, and depth data) associated with each of the images of thesource set to the spatial metadata associated with the 3D model.

After the source-regions have been determined in step 110,classification of the target region is adjusted based on classificationsassigned to the source-regions. Specifically, the classificationsassigned to the source regions may be aggregated to produce an aggregateclassification. The aggregate classification may be assigned to thetarget portion of the 3D model. The aggregate classification may then beback-projected to the target region (and, optionally, to regions inother photos that correspond to the target portion of the 3D model). Forexample, assume that “bedroom” has the highest score in the room-typeclassifications in majority of images A to H. Under these circumstances,the aggregate room-type classification may be determined to be“bedroom”, and the room-type classification for photo-realistic image Amay be changed to “bedroom”.

The classification adjustment made in step 112 may be more sophisticatedthan simply adopting the classification made for the majority ofsource-regions. For example, in the case of room-type classifications,the room-type classification of photo-realistic image A may be changedto be the average of the room-type classifications of all source-regionsthat depict room X. As another example, the classification confidencesfrom the source-regions may be combined in a more sophisticated mannerdescribed in the following section.

Combining Classification Confidences

Classifiers may have built-in biases. For example, a classifier that hasbeen trained to assign “room-type” classifications to views may have abias towards the “bedroom” label because bedrooms are the most commontype of room in most residential homes. In situations where such biasesexist, merely taking the arithmetic or geometric mean over theclassifications of the source-regions (in this case, the views of theroom that is being classified) may magnify the prior bias.

To avoid that outcome, Bayes' formula may be applied as describedhereafter. Assume that the initial classifier for each picture Di androom class r indicates a probability of room belonging to that class:p(r|D _(i))

The goal is to find a combined probability across several differentpictures:p(r|D ₁ . . . D _(n))

According to Bayes:

${p\left( {r❘{D_{1}\ldots D_{n}}} \right)} = \frac{{p\left( {{D_{1}\ldots D_{n}}❘r} \right)}{p(r)}}{p\left( {D_{1}\ldots D_{n}} \right)}$

Assuming that images like D1 and Dn are conditionally independent givenr, this can be rewritten:

${p\left( {r❘{D_{1}\ldots D_{n}}} \right)} = \frac{{p\left( {D_{1}❘r} \right)}\ldots{p\left( {D_{n}❘r} \right)}{p(r)}}{p\left( {D_{1}\ldots D_{n}} \right)}$

While it is unlikely that images D1 and Dn are entirely conditionallyindependent given r, making this assumption produces a reasonableapproximation. Based in this assumption, Bayes' rule can be appliedagain to produce:

${p\left( {r❘{D_{1}\ldots D_{n}}} \right)} = \frac{{p\left( D_{1} \right)}\ldots{p\left( D_{n} \right)}{p\left( {r❘D_{1}} \right)}\ldots{p\left( {r❘D_{n}} \right)}{p(r)}}{{p(r)}^{n}{p\left( {D_{1}\ldots D_{n}} \right)}}$

Observing that the sum of all probabilities equals to one:

${\sum\limits_{r}{p\left( {r❘{D_{1}\ldots D_{n}}} \right)}} = 1$

for each r, probability may be computed as:

$p_{r} = \frac{{p\left( {r❘D_{1}} \right)}\ldots{p\left( {r❘D_{n}} \right)}}{{p(r)}^{n - 1}}$

This can be normalized to 1:

${p\left( {r❘{D_{1}\ldots D_{n}}} \right)} = \frac{p_{r}}{\sum\limits_{r}p_{r}}$

As an example, assume that this formula is applied to a situation wherethere are 10 pictures (source-regions) of a room. For each picture,assume that the classifier says that it's a bedroom with 90%probability, but a pool room (billiards) with 10% probability. Fromprior determinations, it is known that usually 20% of rooms are ourbedrooms and only 1% are pool rooms. Applying the formula to thatsituation, the combined confidence would be that there is a 99.3%probability that the room in question (the target portion of the 3Dmodel) is a pool room.

In one embodiment, this classification aggregation formula is enhancedby weighting the classification probabilities from source regions'classifications based on distance from camera center to mesh face, andangle between face normal and vector from camera center to facecentroid. Thus, a face seen in the photo-realistic image that is faraway and at a sharp angle will get less weight in the aggregatedclassification than a face that is closer and facing the camera. Itshould be noted that in aggregating classifications, such weightadjustments are optional, and the factors used to adjust weights mayvary based on the nature of the item being classified. Other suchfactors include, but are not limited to, the percentage of theroom/object that appears in the image, how close a view the image has ofthe room/object, etc.

Fine Granularity Example

Steps 104 to 112 may be repeated for any number of target regions of anynumber of target photo-realistic images. As mentioned above, the targetregion selected in step 104 may be as large as an entire panoramicphoto-realistic image, or as small as a pixel. As another example of thetechnique illustrated in FIG. 1 , assume that that target regionselected in step 104 is a set of pixels, within photo-realistic image A,that depict an object X. Further assume that, within photo-realisticimage A, object X has been classified as a table.

At step 106, the portion of the 3D model that maps to the target regionis determined. In the present example, since the classification at issueis object-specific classification, the target portion of the 3D model isthe object, within the model, that represents object X. Determining theportion of the 3D model that maps to the target region may be complex.For example, assume that the target region depicts a portion of a table.A table has many sides, and the portion of the table that is depicted inthe target region may only be a fraction of the table. Different imageswill see different parts of the same table. Thus, according to oneembodiment, a model-centric segmentation is performed to separate thetable from other portions of the model. After performing a model-centricsegmentation, step 106 may be performed based, in part, on themodel-centric segmentation.

At step 108, the “source-set” for the target portion of the 3D model isdetermined. In the present example, the target portion of the 3D modelis the representation of object X. For the purpose of explanation, itshall be assumed that the source-set of object X includesphoto-realistic images A, B and C. Once the source-set of the targetportion of the model has been determined at step 108, the“source-regions” within the source-set photo-realistic images areidentified. In the present example, it is determined which pixels,within photo-realistic images A, B, and C, depict object X.

After the source-regions have been determined in step 110,classification of the target region is adjusted based on classificationsof assigned to the source-regions. As mentioned above, adjusting theclassification of the target region may involve generating an aggregateclassification using simple or complex aggregation techniques. As asimple aggregation example where “majority rules”, if the source-regionsof photo-realistic images B and C has been classified as depicting“couch”, then the classification of the target region in photo-realisticimage A may be changed from “table” to “couch”.

It should be noted that a classifier that outputs a category could berun just on each source region, or a per-pixel classifier could be runon the whole image containing the source region. In the latter case, theclassification for any given source region could be an amalgamation ofthe classifications of the pixels in the region.

Variations

The steps illustrated in FIG. 1 are merely an example of how oneembodiment may adjust classifications. Other embodiments may modify thesequence of steps to arrive at similar results. For example, rather thanautomatically classify all photo-realistic images in step 102, theautomatic classification may be performed only on the targetphoto-realistic image (after step 104), and on the source-set of thetarget portion of the 3D model (after step 110).

As another example, when the classification of a feature is adjusted onthe target photo-realistic image, the classification of the same featuremay undergo the same adjustment on all other photo-realistic images inthe source-set of that feature. For example, assume that the same objecthas been classified as a window in three photo-realistic images, as adoor in one photo-realistic image, and as a painting in fivephoto-realistic images. Under these circumstances, step 112 may involveadjusting the classification of the object in all nine photo-realisticimages to indicate that the object is a painting.

The classification step may also include a classification step baseddirectly on the 3D model itself. Machine learning algorithms or otheralgorithms may make a classification judgement based on the 3D model'sgeometry, its appearance, the square footage of a room, the shape of aroom, or other properties. Individual images' classifications may serveas inputs to this 3D model-based classifier. One example of a 3Dmodel-based classifier that runs on voxels:stanford.edu/˜rezab/papers/fusionnet.pdf.

Automated Labeling of 3D Model Segments

Once a 3D model has been segmented (either manually or by using anautomated segmentation technique), it is often useful to tag eachsegment with appropriate metadata. For example, in the case of a 3Dmodel of a house that has been segmented into rooms, it is oftendesirable to tag the rooms with metadata that indicates the appropriateroom-type (kitchen, bathroom, dining room, etc.). An example of how 3Dmodel segmentation may be performed shall now be given with reference toFIGS. 2-4 .

As mentioned above, a 3D model of a real-world space may be constructedbased on panorama images of known locations/poses throughout the space.FIG. 2 is an example of a panoramic view of the interior of a house. Forthe purpose of explanation, it shall be assumed that the panoramic viewillustrated in FIG. 2 is one photo-realistic image of a collection ofphoto-realistic images that is used to construct a 3D model of “houseX”.

As part of the construction of the 3D model, a mesh for the space mayalso be created. With a virtual camera, views can be generated from anypanorama for any field of view, roll and yaw and almost any pitch. Sincethe panorama images have known locations/poses, it is possible toautomatically determine that a plurality of views are looking at thesame part of the mesh. FIG. 3 illustrates six views from differentpanoramas of the same part of the mesh of house X.

According to an embodiment, the system back-projects from each view tothe mesh and finds, at some granularity (e.g. on a mesh-face bymesh-face basis), which part of the mesh is visible for the view. Theprocess of finding the part of the mesh that is visible for the view isan example of step 106, where the “target region” is the view inquestion.

In the present example, the goal is to apply accurate labelling toportions of the 3D model itself. Therefore, once the view-to-facemapping is determined for the various views of the house, the systemassigns room labels to each face in the mesh based on the classificationof the different views that map to the face. For example, the room-typeclassifications that have already been assigned to the views in FIG. 3are assigned to the faces of the room, within the 3D model, that aredepicted in those views.

FIG. 4 illustrates the mesh of house X after the room-typeclassifications of views have been projected onto the correspondingfaces of the mesh. For the purpose of illustration, the room-typeclassifications assigned to each face in the mesh is illustrated by thecoloring of the face of the mesh, where the degree to which a facereflects a particular color indicates the degree to which the face hasbeen classified as the room-type to which that color is assigned. In theillustrated example, blue is assigned to “dining room” and the faces ofroom 400 are predominantly blue, indicating that the views that map toroom 400 of the 3D model were predominantly classified as “dining room”.

Similarly, green has been assigned to “living room” and the faces ofrooms 402, 404 and 406 are predominantly green, indicating that theviews that map to those rooms were predominantly classified as “livingroom”. Red has been assigned to “kitchen” and the faces of room 408 arepredominantly red, indicating that the views that map to room 408 werepredominantly classified as “kitchen”.

Using multiple views/classifications per mesh face increases accuracy ofthe classification of the mesh face. For example, one or more views ofroom 408 may have been labeled “dining room”. However, because all viewsof room 408 were taken into account when projecting labels onto thefaces of room 408, room 408 (and the mesh faces thereof) are moreaccurately labeled “kitchen”.

Face-to-View Projection

Once faces in the mesh have been classified from multiple views, thesystem can project from faces in the mesh back to views and get aper-view classification that has higher accuracy compared to theclassification of the original view. This process is equivalent to step112 of FIG. 1 , since the classifications that have been assigned toeach mesh face are an aggregation of the classifications of the “sourceregions” of the mesh face.

FIG. 5 is a view that was initially classified as depicting a “kitchen”with a classifier confidence of 87%. However, after adjusting theroom-type classification of view based on the classifications that wereassigned to the mesh faces that map to the view (which are mesh faces ofin room 408 of FIG. 4 ), the room-type classification of the view isadjusted to be “kitchen” with a 99.4% classifier confidence.

Improved Segmentation of 3D Models

Improving the accuracy of target region/view classifications is merelyone of many benefits for assigning classifications to portions of a 3Dmodel using the techniques described herein. Another use is to improvethe segmentation of the 3D model itself. Specifically, varioustechniques can be used to segment 3D models, including but not limitedto computational geometry based approaches. Such techniques may be used,for example, to divide the 3D model of house X, illustrated in FIG. 4 ,into rooms.

However, such segmentation may be improved by using the classificationsassigned to portions of the 3D model as a factor in deciding how tosegment the 3D model. For example, prior to projecting room-typeclassifications to the faces of house X illustrated in FIG. 4 , thespace containing rooms 400 and 404 may have been treated as a singleroom. However, after the room-type classifications have been projectedto the faces of house X, it is clear that the space in question is moreaccurately treated as two rooms, one whose faces were predominantlyclassified at dining room (room 400), and one whose faces werepredominantly classified as living room (room 404). Thus, the faceclassifications may be used in conjunction with any other segmentationtechnique to improve the accuracy of the segmentation.

Determining “Best Views” of a Real-World Space

It is often desirable to identify which photo-realistic images, from alarge collection, represent the “best views” of a real-world space, asdefined by a user's experience of aesthetic value, informativeness, orother characteristics. For example, when advertising a house for sale,few potential buyers are willing to wade through a collection of 1000photo-realistic images of the house. It is much preferable to present topotential buyers one or two of the best photo-realistic images of eachroom of the house. The actual number to present may vary based on thetype of the room. For example, it is often desirable to have morephoto-realistic images of the kitchen and fewer photo-realistic imagesof a walk-in closet.

A collection of images of a building may be created by takingequally-angularly-spaced snapshots from every panographic image that wasused to create a 3D model of the building. Various techniques areavailable for automatically determining the “best views” from such acollection of views. For example, numerous computer vision techniqueshave been used to determine what constitutes a good view. Suchtechniques typically take into account visual heuristics, such as imageand depth characteristics. By way of example, but not limitation,computer vision techniques for determining what constitutes a good viewinclude any combination of:

1—Casting rays and find the length of the rays (directly from cameradepth data or from synthetic depth data from mesh) to calculate the viewvolume. Greater volume is better.

2—Calculating the variance of the lengths of neighbor rays. Greatervariance is better.

3—Calculating mesh normal variance (similar to 2). Greater variance isbetter.

4—Calculating the variance of the colors of neighbor pixels. Greatervariance is better. This can be done by blurring image A to get image B.Subtract image A from image B to get image C. Find the sum of theabsolute values of image C.

5—The output of a machine learning algorithm trained to recognizedesirable (e.g. aesthetically pleasing) views based on a corpus oftraining examples.

It should be noted that using either 1, 2, 3 or 4 alone preventsselection of an image of a flat, solid colored wall viewed from a shortdistance.

According to one embodiment, the techniques described herein may be usedin conjunction with existing “best view” selection techniques in avariety of ways. For example, after adjusting the room-typeclassifications of views using the techniques described herein, thoseimproved room-type classifications may be used as a factor indetermining photo-realistic image quality, where the higher theconfidence of the room-type classification the higher the quality score.Specifically, if the best “kitchen” photo-realistic image is beingselected, then the views with higher confidence scores of being akitchen probably contain more of the things that make a room a kitchen(e.g. stove, oven, etc.). Therefore, rooms with higher confidence scores(as adjusted using the techniques described herein) for the room-type inquestion are considered to be better than photo-realistic images withlower confidence scores for that type of room.

Classifications that have been adjusted/improved using the techniquesdescribed herein may also be used to determine which photo-realisticimages each photo-realistic image is compared against (e.g. the qualityscores of “kitchen” photo-realistic images are compared against thequality scores of other “kitchen” photo-realistic images whendetermining the “best photo-realistic images” for the kitchen).

Those same classifications may be used in selecting a caption to displayin conjunction with an image. For example, a photo-realistic image withan adjusted confidence score of 98% for the label “kitchen” may beassigned the caption “kitchen” to be displayed in conjunction with thephoto-realistic image itself.

Quality measures that are based on classifications that have beenimproved using the techniques described herein may also serve as thebasis for selecting which photos/views to include in a virtual tour ofthe house. For example, a virtual tour of a house is typically a videoor sequence of images that “walks” the viewer through the house. As thetour visits each room, it is desirable that the tour move to a positionto display the “best” view(s) of the room. Consequently, classificationsthat have been adjusted using the techniques described herein may beused to (a) determine the segmentation between rooms, (b) the type ofroom associated with each image, and (c) which points of view or photosqualify as “best” for each given room.

Synthetic Viewpoints

In the examples given above, the photo-realistic images that areclassified and whose classifications are projected onto thecorresponding portions of the 3D model are the photo-realistic images ofthe real-world space represented by the 3D model. However, once the 3Dmodel is created based on such real-world photo-realistic images, it ispossible to render synthetic viewpoints based on the 3D model. Suchsynthetic viewpoints may be classified in the same manner as thereal-world photo-realistic images. Specifically, those syntheticviewpoints may be fed to a machine learning engine that has been trainedto classify photo-realistic images (e.g. assign room-type probabilitiesto the photo-realistic images). Once the synthetic viewpoints have beenclassified in this manner, the classifications of the syntheticviewpoints may be projected onto the 3D model in the manner discussedabove. Those projected classifications may be combined in the samemanner as described above, and may be used to improve segmentation ofthe model and/or the classifications assigned to the syntheticviewpoints.

Hardware Overview

According to one embodiment, the techniques described herein areimplemented by one or more special-purpose computing devices. Thespecial-purpose computing devices may be hard-wired to perform thetechniques, or may include digital electronic devices such as one ormore application-specific integrated circuits (ASICs) or fieldprogrammable gate arrays (FPGAs) that are persistently programmed toperform the techniques, or may include one or more general purposehardware processors programmed to perform the techniques pursuant toprogram instructions in firmware, memory, other storage, or acombination. Such special-purpose computing devices may also combinecustom hard-wired logic, ASICs, or FPGAs with custom programming toaccomplish the techniques. The special-purpose computing devices may bedesktop computer systems, portable computer systems, handheld devices,networking devices or any other device that incorporates hard-wiredand/or program logic to implement the techniques.

For example, FIG. 6 is a block diagram that illustrates a computersystem 600 upon which an embodiment of the invention may be implemented.Computer system 600 includes a bus 602 or other communication mechanismfor communicating information, and a hardware processor 604 coupled withbus 602 for processing information. Hardware processor 604 may be, forexample, a general purpose microprocessor.

Computer system 600 also includes a main memory 606, such as a randomaccess memory (RAM) or other dynamic storage device, coupled to bus 602for storing information and instructions to be executed by processor604. Main memory 606 also may be used for storing temporary variables orother intermediate information during execution of instructions to beexecuted by processor 604. Such instructions, when stored innon-transitory storage media accessible to processor 604, rendercomputer system 600 into a special-purpose machine that is customized toperform the operations specified in the instructions.

Computer system 600 further includes a read only memory (ROM) 608 orother static storage device coupled to bus 602 for storing staticinformation and instructions for processor 604. A storage device 610,such as a magnetic disk, optical disk, or solid-state drive is providedand coupled to bus 602 for storing information and instructions.

Computer system 600 may be coupled via bus 602 to a display 612, such asa cathode ray tube (CRT), for displaying information to a computer user.An input device 614, including alphanumeric and other keys, is coupledto bus 602 for communicating information and command selections toprocessor 604. Another type of user input device is cursor control 616,such as a mouse, a trackball, or cursor direction keys for communicatingdirection information and command selections to processor 604 and forcontrolling cursor movement on display 612. This input device typicallyhas two degrees of freedom in two axes, a first axis (e.g., x) and asecond axis (e.g., y), that allows the device to specify positions in aplane.

Computer system 600 may implement the techniques described herein usingcustomized hard-wired logic, one or more ASICs or FPGAs, firmware and/orprogram logic which in combination with the computer system causes orprograms computer system 600 to be a special-purpose machine. Accordingto one embodiment, the techniques herein are performed by computersystem 600 in response to processor 604 executing one or more sequencesof one or more instructions contained in main memory 606. Suchinstructions may be read into main memory 606 from another storagemedium, such as storage device 610. Execution of the sequences ofinstructions contained in main memory 606 causes processor 604 toperform the process steps described herein. In alternative embodiments,hard-wired circuitry may be used in place of or in combination withsoftware instructions.

The term “storage media” as used herein refers to any non-transitorymedia that store data and/or instructions that cause a machine tooperate in a specific fashion. Such storage media may comprisenon-volatile media and/or volatile media. Non-volatile media includes,for example, optical disks, magnetic disks, or solid-state drives, suchas storage device 610. Volatile media includes dynamic memory, such asmain memory 606. Common forms of storage media include, for example, afloppy disk, a flexible disk, hard disk, solid-state drive, magnetictape, or any other magnetic data storage medium, a CD-ROM, any otheroptical data storage medium, any physical medium with patterns of holes,a RAM, a PROM, and EPROM, a FLASH-EPROM, NVRAM, any other memory chip orcartridge.

Storage media is distinct from but may be used in conjunction withtransmission media. Transmission media participates in transferringinformation between storage media. For example, transmission mediaincludes coaxial cables, copper wire and fiber optics, including thewires that comprise bus 602. Transmission media can also take the formof acoustic or light waves, such as those generated during radio-waveand infra-red data communications.

Various forms of media may be involved in carrying one or more sequencesof one or more instructions to processor 604 for execution. For example,the instructions may initially be carried on a magnetic disk orsolid-state drive of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to computer system 600 canreceive the data on the telephone line and use an infra-red transmitterto convert the data to an infra-red signal. An infra-red detector canreceive the data carried in the infra-red signal and appropriatecircuitry can place the data on bus 602. Bus 602 carries the data tomain memory 606, from which processor 604 retrieves and executes theinstructions. The instructions received by main memory 606 mayoptionally be stored on storage device 610 either before or afterexecution by processor 604.

Computer system 600 also includes a communication interface 618 coupledto bus 602. Communication interface 618 provides a two-way datacommunication coupling to a network link 620 that is connected to alocal network 622. For example, communication interface 618 may be anintegrated services digital network (ISDN) card, cable modem, satellitemodem, or a modem to provide a data communication connection to acorresponding type of telephone line. As another example, communicationinterface 618 may be a local area network (LAN) card to provide a datacommunication connection to a compatible LAN. Wireless links may also beimplemented. In any such implementation, communication interface 618sends and receives electrical, electromagnetic or optical signals thatcarry digital data streams representing various types of information.

Network link 620 typically provides data communication through one ormore networks to other data devices. For example, network link 620 mayprovide a connection through local network 622 to a host computer 624 orto data equipment operated by an Internet Service Provider (ISP) 626.ISP 626 in turn provides data communication services through the worldwide packet data communication network now commonly referred to as the“Internet” 628. Local network 622 and Internet 628 both use electrical,electromagnetic or optical signals that carry digital data streams. Thesignals through the various networks and the signals on network link 620and through communication interface 618, which carry the digital data toand from computer system 600, are example forms of transmission media.

Computer system 600 can send messages and receive data, includingprogram code, through the network(s), network link 620 and communicationinterface 618. In the Internet example, a server 630 might transmit arequested code for an application program through Internet 628, ISP 626,local network 622 and communication interface 618.

The received code may be executed by processor 604 as it is received,and/or stored in storage device 610, or other non-volatile storage forlater execution.

In the foregoing specification, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense. The sole and exclusive indicator of the scope of the invention,and what is intended by the applicants to be the scope of the invention,is the literal and equivalent scope of the set of claims that issue fromthis application, in the specific form in which such claims issue,including any subsequent correction.

What is claimed is:
 1. A method comprising: determining a firstsource-set for a target portion of a 3D-model of a real-world space, the3D-model being based on a first collection of photo-realistic images ofthe real-world space captured during a first period of time, each imagein the first collection of photo-realistic images including spatialmetadata, the first source-set including a subset of the firstcollection of photo-realistic images, the subset of the first collectionof photo-realistic images including a target region to which the targetportion maps; identifying a plurality of source-regions in the firstcollection of photo-realistic images of the first source-set, each ofthe plurality of source-regions being a region within a photo-realisticimage of the first collection of photo-realistic images correspondingthat map to the target portion of the 3D-model; assigning asource-region classification to the plurality of source-regions in thefirst collection of photo-realistic images of the first source-set; andassigning a particular classification to the target region based, atleast in part, on the assigned source-region classification to theplurality of source-regions in the first collection of photo-realisticimages of the first source-set, wherein the method is performed by oneor more computing devices.
 2. The method of claim 1, wherein thedetermining the first source-set for the target portion of the 3D-modelis based on the spatial metadata of the first collection ofphoto-realistic images.
 3. The method of claim 1, wherein theidentifying the plurality of source regions in the first collection ofphoto-realistic images of the first source-set is based on the spatialmetadata of the first collection of photo-realistic images.
 4. Themethod of claim 1, wherein the real-world space is a building and theportion of the 3D-model is the portion of the 3D-model that represents aparticular room of a house.
 5. The method of claim 4, wherein theclassifications assigned to the plurality of source regions areroom-type classifications and the particular classification assigned tothe target region is a room-type classification.
 6. The method of claim5 further comprising, determining, based at least in part on theparticular classification, that the particular photo-realistic imageshould be used as a best photo of the particular room.
 7. The method ofclaim 6 further comprising including the particular photo-realisticimage in a virtual tour of the building based on the particularphoto-realistic image being determined to be a best photo of theparticular room.
 8. The method of claim 1, wherein at least onesource-region of the plurality of source regions is a set of pixelswithin a photo-realistic image from the first collection ofphoto-realistic images.
 9. The method of claim 1, further comprisingdetermining the one of the subset of the collection of photo-realisticimages based on a view volume of each of the subset of the collection ofphoto-realistic images and calculating a variance of colors ofneighboring pixels of each of the subset of the collection ofphoto-realistic images.
 10. The method of claim 1 wherein assigning theparticular classification to the target region comprises: aggregatingthe classifications assigned to the plurality of source-regions togenerate an aggregate classification; assigning the aggregateclassification to the portion of the 3D model; and determining theparticular classification based, at least in part, on the aggregateclassification.
 11. The method of claim 1 further comprising:determining a second source-set for the target portion of the 3D model,the second source-set including a second collection of photo-realisticimages of the real-world space capture during a second period of time;identifying a plurality of source-regions in the second collection ofphoto-realistic images of the second source-set, each of the pluralityof source-regions being a region within a photo-realistic image of thesecond collection of photo-realistic images corresponding to the targetportion of the 3D-model; assigning a source-region classification to theplurality of source-regions in the second collection of photo-realisticimages of the second source-set; and if the source-region classificationto the plurality of source-regions in the second collection ofphoto-realistic images of the second source-set is identical to thesource-region classification to the plurality of source-regions in thefirst collection of photo-realistic images of the first source-set, thenreassign a particular classification to the target region based, atleast in part, on the assigned source-region classification to theplurality of source-regions in the second collection of photo-realisticimages of the second source-set.
 12. One or more non-transitorycomputer-readable media storing instructions which, when executed by oneor more computing devices, cause the one or more computing devices toperform: determining a first source-set for a target portion of a3D-model of a real-world space, the 3D-model being based on a firstcollection of photo-realistic images of the real-world space capturedduring a first period of time, each image in the first collection ofphoto-realistic images including spatial metadata, the first source-setincluding a subset of the first collection of photo-realistic images,the subset of the first collection of photo-realistic images including atarget region to which the target portion maps; identifying a pluralityof source-regions in the first collection of photo-realistic images ofthe first source-set, each of the plurality of source-regions being aregion within a photo-realistic image of the first collection ofphoto-realistic images corresponding to the target portion of the3D-model; assigning a source-region classification to the plurality ofsource-regions in the first collection of photo-realistic images of thefirst source-set; and assigning a particular classification to thetarget region based, at least in part, on the assigned source-regionclassification to the plurality of source-regions in the firstcollection of photo-realistic images of the first source-set.
 13. Theone or more non-transitory computer-readable media of claim 12, whereinthe determining the first source-set for the target portion of the3D-model is based on the spatial metadata of the first collection ofphoto-realistic images.
 14. The one or more non-transitorycomputer-readable media of claim 12, wherein the identifying theplurality of source regions in the first collection of photo-realisticimages of the first source-set is based on the spatial metadata of thefirst collection of photo-realistic images.
 15. The one or morenon-transitory computer-readable media of claim 12, wherein theclassifications assigned to the plurality of source regions areroom-type classifications and the particular classification assigned tothe target region is a room-type classification.
 16. The one or morenon-transitory computer-readable media of claim 15 wherein theinstructions, when executed by one or more computing devices, furthercause, determining, based at least in part on the particularclassification, that the particular photo-realistic image should be usedas a best photo of the particular room.
 17. The one or morenon-transitory computer-readable media of claim 12, wherein theinstructions, when executed by one or more computing devices, furthercause: aggregating the classifications assigned to the plurality ofsource-regions to generate an aggregate classification; assigning theaggregate classification to the portion of the 3D model; and determiningthe particular classification based, at least in part, on the aggregateclassification.
 18. The one or more non-transitory computer-readablemedia of claim 12, wherein the instructions, when executed by one ormore computing devices, further cause: determining a second source-setfor the target portion of the 3D model, the second source-set includinga second collection of photo-realistic images of the real-world spacecapture during a second period of time; identifying a plurality ofsource-regions in the second collection of photo-realistic images of thesecond source-set, each of the plurality of source-regions being aregion within a photo-realistic image of the second collection ofphoto-realistic images corresponding to the target portion of the3D-model; assigning a source-region classification to the plurality ofsource-regions in the second collection of photo-realistic images of thesecond source-set; and if the source-region classification to theplurality of source-regions in the second collection of photo-realisticimages of the second source-set is identical to the source-regionclassification to the plurality of source-regions in the firstcollection of photo-realistic images of the first source-set, thenreassign a particular classification to the target region based, atleast in part, on the assigned source-region classification to theplurality of source-regions in the second collection of photo-realisticimages of the second source-set.
 19. A hardware server comprising: amemory storing computer-executable components; and a processorconfigured to execute the computer-executable components to perform:determining a first source-set for a target portion of a 3D-model of areal-world space, the 3D-model being based on a first collection ofphoto-realistic images of the real-world space captured during a firstperiod of time, each image in the first collection of photo-realisticimages including spatial metadata, the first source-set including asubset of the first collection of photo-realistic images, the subset ofthe first collection of photo-realistic images including a target regionto which the target portion maps; identifying a plurality ofsource-regions in the first collection of photo-realistic images of thefirst source-set, each of the plurality of source-regions being a regionwithin a photo-realistic image of the first collection ofphoto-realistic images corresponding to the target portion of the3D-model; assigning a source-region classification to the plurality ofsource-regions in the first collection of photo-realistic images of thefirst source-set; and assigning a particular classification to thetarget region based, at least in part, on the assigned source-regionclassification to the plurality of source-regions in the firstcollection of photo-realistic images of the first source-set.